What does pci_map_single do

[shesha bhushan]

Hi All,

I wanted to use DMA in my device driver.

1. pci_map_single will transfer the data from RAM (kernel area) to the 
hardware accessible area and will provide with a pointer which can then be 
passed to the hardware.
2. In the above function the "size" parameter indicates the amount of DMA 
transfer.
Am I correct in the above two points? If I am wrong please correct me.

In the Linux Device driver book (page 408), he says, data must be explicitly 
flushed from the processor cache. And data flushed this way is not avaliable 
to the device.

This means that we must flush the processor cache before calling 
pci_map_single. How can we achieve this.

Thanking You
Shesha

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